In the recovery of precious metals (such as PGMs), every fraction of a percentage improvement in the technical metal recovery efficiency (amount of PGM recovered as a percentage of PGM input processed) has a profound impact on the commercial performance and competitiveness of the process. This is because the operators pay considerable amounts for the ‘waste’ in the first place, the margins are modest and the working capital requirements and risks are high.
GB2465603 discloses a plasma assisted PGM recovery process. The technical metal recovery efficiency for a system as described in GB2465603 is high compared to other competing technologies. Single pass recovery efficiencies of around 98% w/w have been achieved. Furthermore, the technology disclosed in this application offers an advantage in that the configuration of the plasma based heating system leads to lower physical and chemical carryover of dust into the off-gas abatement system and, therefore, lower losses of PGMs.
In order to meet the required environmental compliance targets, the off-gas stream from the thermal process must be contained and treated prior to discharge. This includes dosing with sorbents in a dry scrubber (a high temperature ceramic filter). The combined action of the sorbent and filter captures airborne pollutants, such as a fly ash and salt by-products produced during scrubbing (sulphates, oxides, chlorides). The design disclosed in GB2465603 allows for simultaneous gas cleaning and particulate removal in a single filtration unit.
U.S. Pat. No. 4,295,881 discloses a process for the recovery of PGMs from chromite based ores that is reliant on high intensity smelting operations described in U.S. Pat. No. 4,685,963. U.S. Pat. No. 4,295,881 states that the process off-gas can be passed through a baghouse to recover airborne dust. This dust can then be treated by conventional lead blast furnace practice.